The present invention is directed to a vibratory compactor used, for example, to compact backfilled trenches after a pipeline is laid or to compact the floor of a trench or to compact asphalt or larger areas, and more particularly, relates to steering for a vibratory compactor of the above-mentioned type.
Vibratory compactors are used in a variety of ground compaction and ground leveling applications. Most vibratory compactors have plates or rollers that rest on the surface to be compacted and that are excited to vibrate so as to compact and level a worked surface. A common vibratory compactor, and one to which the invention is well-suited, is a vibratory trench roller.
The typical vibratory trench roller includes a chassis supported on the surface to be compacted by front and rear rotating drum assemblies. Each drum assembly supports a respective subframe of the chassis if the trench roller is an articulated trench roller. The subframes may be articulated to one another by a pivot connection. Each of the drum assemblies may include a stationary axle housing and a drum that is mounted on the axle housing and that is driven to rotate by a dedicated hydraulic motor. Hydraulic motors are typically supplied with pressurized hydraulic fluid from a pump which may be powered by an engine mounted on one of the subframes.
Each drum may be excited to vibrate by a dedicated exciter assembly that is located within the associated subframe and is powered by a motor connected to a pump. The exciter assembly typically comprises one or more eccentric masses mounted on a rotatable shaft positioned within the subframe. Rotation of the eccentric shaft imparts vibrations to the subframe and to the remainder of the drum assembly. The entire machine may be configured to be as narrow as possible so as to permit the machine to fit within a trench whose floor is to be compacted. Machine widths of less than 3 feet (1 meter) are common. Vibratory trench rollers of this basic type are disclosed, e.g., in U.S. Pat. No. 4,732,507 to Artzberger; U.S. Pat. No. 4,793,735 to Paukert; U.S. Pat. No. 5,082,396 to Polacek; U.S. Pat. No. 7,059,802 to Geier et al.; and U.S. Pat. No. 8,585,317 to Sina, the entireties of which are hereby expressly incorporated by reference thereto.
Vibratory roller machines with articulated steering are advantageous in that their movement permits changes in direction during normal travel, or small corrections in direction, to be rapidly undertaken without damaging the already compacted surface of the ground. To effect such changes in direction, the typical articulated steering system employs an extensible linear steering actuator mounted between the subframes and a solid axle configuration connecting left and right drum halves. A hydraulic cylinder is employed in most instances. Steering is affected by linearly extending or retracting the steering actuator to cause the front subframe to pivot about the machine's longitudinal centerline and alter the articulation angle between the front and rear subframes.
However, high pressure steering actuators are costly and are prone to failure, such as by way of oil leaks and/or pressure losses. Electrically powered high force actuators suitable for steering are available, but are more costly than hydraulic actuators. And they have many moving parts which are prone to failure in severe operating conditions. Also, solid axle configurations may impede steering function and precision and may cause the drums to scratch and/or deform finished surfaces when steering to the left or right. In addition, vibratory roller machines with linear steering actuators and solid axle configuration are further limited by the maximum slope in which they can traverse. The need therefore exists to provide a system for a vibratory roller machine that eliminates one or more of the foregoing disadvantages.